Modulation system for ultra-high frequency waves



May 18, 1937., H. E. HOLLMANN MODULATION SYSTEM FOR ULTRA HIGH FREQUENCY WAVES Filed Aug. 15. 1935 INVENTOR. A .HANS ERICH HOLLMANN BY 7 g-Wv' Z ATTORNEY.

Patented May 18, 1937 UNITED STATES PATE --; orrlcs MODULATION SYSTEM FOR ULTRA-HIGH FREQUENCY WAVES Hans Erich Hollmanrl, Berlin,

Germany, as-

Application August 15, 1935, Serial No. 36,309 In Germany August 21, 1934 6 Claims.

This invention relates to generators of modulated ultra-high frequency energy and has particularly to do with provision of improved means for applying modulation to such a generator. In my copending application, Serial No. 36,308, filed August 15, 1935, I have described a system having objects similar to those which will presently be set forth in respect to this invention. In that copending application I oifered a solution to the 10 problem of applying modulation frequencies to an ultra-high frequency generator in which different anode segments of a split anode magnetron structure were respectively connected in parallel to the output circuits of as many electron discharge tubes. The modulation frequencies were then applied in a push-pull manner to the input circuits of these electron discharge tubes.

An alternative arrangement is set forth in the instant application wherein only one modulation tube is employed, and this is preferably inserted as a sort of bridge across the leads to the respective split anode segments of a magnetron oscillator or, if desired, an oscillator of the Barkhausen-Kurz type.

The magnetron, as is known, is extremely well suited for producing ultra-short waves, and especially favorable useful effects are obtained therewith where the anode cylinder is divided into two or several segments. In a simple magnetron, 3O modulation fluctuations may be superposed on the direct plate potential. In the case of a split anode magnetron with two segments, or in case of a magnetron having a plurality of splits in the anode and two groups of segments, connected in 35 both cases to the two poles of a resonance system, there is obtained a more favorable stabilization of the modulation characteristic and a greater range of control, if the two segments or the two groups of segments instead of being modulated in equal phase, are modulated in push-pull. This was hitherto done in such a manner that two modulation voltages with a phase displacement of 180 such as furnished for instance by a push-pull transformer, were superposed on the 45 equal potentials applied to the two segments, or

groups of segments respectively.

This hitherto known method of modulation implies all the disadvantages encountered in the direct anode potential modulation of any transmitter. Moreover, these secondary windings of the push-pull transformer are highly loaded by the inner resistances of the magnetron, thus requiring considerable modulation energies to produce the alternating potentials necessary for 55 full control of the magnetron, A further drawback is to be seen in the fact that the secondary windings must carry a considerable direct current load to the anode. Hence a transformer of large dimensions is necessary, otherwise the ohmic resistance loss would be excessive.

It is an object of my invention to avoid the above mentioned drawbacks by providing means including a single electron discharge tube bridging the two anode leads of a magnetron oscillator, and thus to superimpose modulation fre- 10 quencies upon the tuned anode circuit of such an oscillator or its equivalent in case a Barkhausen- Kurz tube were to be used.

In carrying out my invention I have found it preferable to employ an electron discharge tube 15 in circuit with the anode leads to a magnetron oscillator, the connections thereto being such that the modulation frequencies will be applied in a push-pull manner to the respective segments or groups of segments of the split anode structure. The alternating voltages furnished at the input circuit of the modulation tube are thus amplified upon being impressed upon the anode segments of the ultra-high frequency oscillator tube.

Such an arrangement requiresspecial consideration to be given to the voltage differences which must be employed between the anode and cathode of the modulation tube and voltage compensating means in the anode leads to the ultrahigh frequency oscillator in order that this oscil- 3O lator may not be unduly unbalanced.

The sole figure of the drawing illustrates diagrammatically a preferred embodiment of my invention and reference will now be had to this figure for a full explanation of the nature of the invention itself, and its mode of operation.

A magnetron type of electron discharge tube M is shown having a cylindrical arrangement of split anodes S1 and S2. The filament cathode K is centrally disposed with respect to the cylindrical system of anode segments. It will be understood that the cathode has two terminals in order that a source of potential may be applied thereto for heating the same. This, however, has not been shown in the drawing because it is well understood by those skilled in the art.

Each of the anode sectors S1 and S2 may be fed with direct current from a source of potential including, say, two series connected batteries 5 and 6. The negative side of the battery 5 is connected to the cathode K. The connection between the batteries 5 and G is connected through a resistor 4 and a choke l to the anode segment S1. The positive pole of the battery 6 is con- 55 A modulator tube R is shown" with iits' anode connected to the direct current plate leadwhich" feeds energy to the anode segment Sz. The cathode 8 of the tube R connectssimilarly' with the direct current plate lead for feeding energy :to the anode segment S1. suitable drop of direct current potential exists between the plate i and the cathode [of the tube R due to the voltage of the battery '6. In

order, however, that there may not be as greata potential difierence between the segments S1 andSz of the magnetron tube as is developed across the terminals of the battery 6, I preferably insert in the direct current anode leads at suitable points resistors such as 3 and I. The

" resistor 3 produces a voltage drop between the anode I of the tube R and the anode segment S2 of the tube M. Since the cathode 8 of the tube-R isnormally at the same potential as that of the anode segment 81 it willv be seen that I can, if desired, make the ohmic resistance value of the resistor 3 substantially intermediate be tween maximum and minimum values of the voltage drop within the tube R. 'Ihisarrangemerit will then restore the balance that is desired between the voltages applied respectively to the anode segments S1 and; S2 and will further provide for the impression of modulating voltages upon the-oscillator tube in a push-pull manner.

The modulator tube R is shown having a cathode heater element 9 which may be fed with alternating current from any suitable source through the transformer T. Modulations from any suitable source may at: the same time be. fed to the input circuit of the tube. R by way of. a transformer T which has=a secondary winding connected atone terminal to the grid 10 and at the opposite terminal through a bias battery ll to the cathode 8.

If the modulations to be impressed upon the oscillation generator are of audio .irequencies, then it is preferable to provide choke coils .I and 2 having iron cores.

In order that'the ultra-high frequency energy may not be unduly impeded by the resistors 3 and 4, these resistors are preferably shunted respectively, in the one case, by a. capacitor C3, and the other case, by .a capacitor C4.

The modulation-circuit functions in such manher that the inner resistance oi. the modulation tube R changes in accordance with the modulation potentials impressed upon the grid circuit of the tube thereby disturbing the equilibrium of :thebridge existing inthe non-modulated state, in, that. the alternating potentials caused at the chokes: i and 2' by the equilibrating currents across the cross resistance of the tube R will be By this arrangement. 2...

modulation potentials impressed upon the input circuit of the tube which comprises the cathode 8, the biasing battery Ii, the secondary winding of the transformer T and the grid ID. The modulation currents, dueto the rectifying action of the tube R, willbe largely in the diration as' indicated by the arrows along side the chokes I .and 2. Hence the modulation voltages impressed upon the anode segments S1 and S2 will be in pmse opposition.

Regarding the size of the modulation tube R it can be said that its inner resistance should be comparative only with the resistance between the plate segments, and that it can be considered as constituted .by the series connection formed by both plate segments and cathode paths. The efjieetive plate potential of the modulation tube R is to be so chosen that the maximum modulation potentials;-. representing only a fraction of. the plate potential, still remain within the linear portion of the characteristic of the tube R. Since, therefore, the plate potential of R can be much lower and the inner resistance greater than in case of ordinary parallel tube modulation, a considerable energy will be consumed by the tube, even in considering the power losses in the resistors 3 and 4 required as compensation for the voltage of the battery}. 7 p

The method according to the invention is not limited to the modulation of a split anode magnetron, but is also capable of effecting the pushpull modulation of two-tubes operating in high frequency push-pull circuit or parallel circuit, whether magnetrons, retardingfleld'h bes, or ordinary triodes in any sen-exciting circuit. circuit shown in the figure isthen only to be mod ified to the extent that in place of the segments 81- and S2 the anodes of the respective generator tubes will be similarly connected to the network.

I claim: I f

1. In an ultra-high frequency oscillator, an electron discharge tube having a centrally disposed cathode and a plurality of cylindric anode segments surrounding the cathode, means includcuit resonant to the operating frequencyoi the oscillator, modulating means including an electron discharge tube the space current path of which is arranged to bridge those two of said circuit leads from the direct current source which are connected respectively with said anode segments, means for enabling'the last said tube to apply modulating potentials contra-phasally to the anode segments of the first saldtube, and a resistive element in one of said circuit leads adaptedto suitably equalize the direct current potentials applied to the anode segments of the first said tube.

2. Ade'vice in accordance with claim 1 and further characterized by having low frequency choke coils in circuit between said direct current source and said Lecher-wire circuit.

'3. An ultra-high frequency oscillator 01 the magnetron type in combination with a Lecherwire system, a source of direct current adapted to feed energy through said system to a plurality of anode segments, said segments being arranged in a cylindrical formation surrounding a centrally disposed cathode in said oscillator, a closed cir- Wit including leads from said direct current source to the two sides of said Lecher-wlre system, an electron discharge tube bridging said leads, and means for applying modulating potentials contra-phasally to said anode segments, said means being simultaneously operative to vary the impedance of the space current path in said closed circuit.

4. A device in accordance with claim 3 and having compensating resistive means for equalizing the direct current potentials applied to said anode segments.

5. In an ultra-high frequency signalling system, an oscillator having a split-anode magnetron discharge tube whose cathode extends coaxially with respect to the anodes, a Lecher-wire system connected to said anodes, means including a source of direct current potential for polarizing said anodes positively with respect to said cathode, said sburce being connectedbetween said cathode and points on said Lecher-wi're system, means bridging the connections to said Lecher-wire system whereby modulating potentials may be applied contra-phasally to said anodes, said means including an electron discharge tube the impedance value of which is under control of a suitable modulation source, and means including series resistors for substantially equalizing the direct current potentials applied to said anodes.

6. A system in accordance with claim 4 and having means for producing a direct current potential drop across the electrodes of the discharge tube in said bridging means.

HANS ERICH HOLLMANN. 

